What is the difference between a Class 2 and Class 3 e-bike?

The three classes are defined as follows:

Class 1: eBikes that are pedal-assist only, with no throttle, and have a maximum speed of 20 mph.

Class 2: eBikes that also have a maximum speed of 20 mph, but are throttle assisted.

Class 3: eBikes that are pedal-assist only, with no throttle and maximum speed of 28 mph.

All classes limit the motor power to 1hp or 750W.

https://peopleforbikes.org/our-work/e-bikes/